Electrochemical Impedance Spectroscopy to Assess Metabolically Active Plaque

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ABSTRACT Cardiometabolic disorders, including hyperlipidemia, obesity, and pre-diabetes, constitute the rising epidemic in the US. These silent disorders progress to chronic diseases, including atherosclerosis. Metabolically active plaques prone to rupture contain high levels of oxidized lipids and M1 macrophages. While rupture of individual plaques is the primary underlying mechanism of myocardial infarction and stroke, real-time detection of the vulnerable plaques prone to rupture remains an unmet clinical challenge. During the previous funding cycle, we demonstrated the sensitivity and specificity of electrochemical impedance spectroscopy for oxidized low density lipoprotein (oxLDL)-laden macrophages (foam cells) in the subendothelial layers of plaques in fat-fed New Zealand White (NZW) rabbits, based on integration of 3 intravascular sensing modalities; namely, shear stress sensor (SSS), ultrasound (IVUS), and electrochemical impedance spectroscopy (EIS). This strategy allowed initial detection in area of disturbed flow, then visualization by IVUS, and then electrochemical characterization by EIS. Vessel walls harboring oxLDL in the macrophages or foam cells exhibit a significant increase in the frequency-dependent EIS magnitude, and these macrophages induce matrix metalloproteinase (MMP) which destabilizes the calcified fibrous cap. We further deployed 3-D EIS sensors in Yucatan mini-pigs undergoing right carotid artery ligation to establish the changes in EIS parameters caused by 12 weeks of high- fat diet. For the next funding cycle, we seek to demonstrate that high 3-D EIS lesions are prone to rupture and embolization. The routine measurement of Fraction Flow Reserve (FFR), defined as the ratio of pressure across the stenotic lesions (Pdownstream/Pupstream) during coronary catheterization, determines the indication for intervention in the significant, ischemia-causing coronary stenoses. For FFR ≥ 0.8, patients are treated with medical therapy; for FFR ≤ 0.8, patients are referred for coronary revascularization. However, the predictors for metabolically active, albeit non-obstructive, lesions prone to rupture remain undefined. In this context, our multi-disciplinary team aims to make the fundamental translation of electrochemical impedance spectroscopy (EIS) in the pre-clinical swine models and to test the hypothesis that 3-D EIS mapping of endoluminal oxLDL- laden macrophages advances our ability to detect human atherosclerotic lesions prone to embolization. To test our hypothesis, we have three Specific Aims. In Aim 1, we will determine in vivo 3-D electrochemical properties to enhance detection of oxLDL-laden plaque. In Aim 2, we will establish 3-D EIS mapping in rupture-prone plaque in swine. In Aim 3, we will compare EIS with near-infrared spectroscopy for oxLDL- laden plaque. Overall, establishing 3-D electrochemical mapping of lipid-laden lesions in a swine model of plaque rupture provides a pre-clinical strategy to identify metabolically active, albeit non-obstructive, lesions, and improve the accuracy of personalized intervention for cardiometabolic disorders.